The present invention relates to a positioning apparatus and method thereof, and an exposure apparatus including the positioning apparatus, and more particularly, to a positioning apparatus which positions a wafer and a mask, and an exposure apparatus including the positioning apparatus.
In the manufacturing process of semiconductor devices such as an IC or an LSI or the like, multiple layers are stacked to form a complete semiconductive device. A pattern to be exposed to a photoresist for forming each of the layers is normally formed on a mask. In order to position each of the layers with high precision, a pattern to be used for forming a next layer must be precisely positioned with a resultant product manufactured in a former process.
Various methods have been suggested as a method for the above described positioning. FIG. 6 shows a positioning method employing two gratings and a detailed description thereof is disclosed in Japanese Patent Application Laid-Open (KOKAI) No. 2-1506.
In the method disclosed in KOKAI No. 2-1506, grating patterns 601 and 602 are established respectively on a mask 603 and a wafer 604 arranged adjacent to each other in an exposure apparatus. A semiconductor laser 606 irradiates the grating pattern 601 with light beam 601. The light beam 607 irradiated by the semiconductor laser 606 is subjected to different diffraction by the two grating patterns 601 and 602, forming two spots on a line sensor 605. Herein, 1 denotes a 1st diffraction and 0 denotes a 0th diffraction, and the diffraction at the time the light beam passing through the mask, the wafer, and the mask is expressed by using these figures. There are two light paths: a light path of 110 diffraction and a light path of 011 diffraction. Because of the presence of these two light paths, the aforementioned two spots are formed. In the above method, the relative amount of position deviation between the mask 603 and wafer 604 is obtained on the basis of the difference in the centroid of the two spots, and positioning is performed in accordance with the amount of position deviation.
However, in the conventional method of positioning shown in FIG. 6, if the gap G between the mask 603 and wafer 604 changes, the centroid of the spot formed on the line sensor 605, which serves as an alignment sensor would change; resulting in deteriorated precision in measuring the relative amount of position deviation between the mask 603 and wafer 604. The deteriorated precision in measurement causes imprecise positioning.
The change in gap G depends upon the precision of a driving apparatus, which adjusts the gap. Moreover, the precision in measurement depends upon mechanical preciseness of an alignment head which detects the centroid of the spot, and the difference in magnification or interference related to two diffraction, the 110 diffraction and 011 diffraction, each forming a respective spot. Furthermore, in a case where the position of a beam irradiating the mask 603 changes relative to the mask 603, the centroid of the spot would also change, resulting in deteriorated precision in measurement of a relative amount of position deviation between the mask 603 and wafer 604.
Due to a complicated physical phenomena in an optical system, the above described factors e.g. the deviation of the gap G, a position deviation of the light beam, and the like, non-linearly influence the precision in measuring the relative amount of position deviation between the mask 603 and wafer 604, thus it is difficult to obtain a correction amount to cancel the influence.
With respect to a method of correcting the amount of alignment, Japanese Patent Application Laid-Open (KOKAI) No. 1-207604 suggests a method utilizing fuzzy inference. FIG. 7 shows the principle of correction utilizing the method. In this method, the amount of correction .DELTA.AA is obtained by adding a correction amount .DELTA.AA1, calculated on the basis of a deviation .DELTA.G of the gap G between the mask 603 and wafer 604, and a correction amount .DELTA.AA2, calculated on the basis of a relative amount (M/P) of a position deviation of the light beam irradiating upon the mask 604.
However, generally the correction amounts for each .DELTA.G and M/P cannot be individually treated, and the influence caused by both amounts interfere with each other. Because of this reason, it is difficult to improve precision of alignment by correcting the amount of alignment, utilizing such simple a equation shown in FIG. 7.